Biomarker comparison

AST vs ALT: what the difference is, and what the AST/ALT ratio means

Short answer

AST and ALT are both enzymes released when cells are injured, and both rise with liver damage — but ALT is concentrated in the liver while AST is also abundant in muscle, heart, kidney and red cells, so ALT is the more specific liver test and AST the one more often raised by something else (a hard workout, a hemolyzed sample, muscle disease). The ratio between them carries information of its own: an AST roughly twice the ALT suggests alcohol-related liver disease, an ALT higher than AST is the usual pattern of fatty liver and viral hepatitis, and the ratio climbs above 1 as scarring advances from any cause.

Medically reviewed by Youmna DiStefano, MD · Last reviewed November 2026

AST vs ALT side by side

	AST	ALT
Full name	Aspartate aminotransferase (formerly SGOT)	Alanine aminotransferase (formerly SGPT)
Normal range (adults)	Male, age 18+: 8 – 48 U/L; Female, age 18+: 8 – 43 U/L	Male, age 18+: 7 – 55 U/L; Female, age 18+: 7 – 45 U/L
Where it is found	Liver, heart, skeletal muscle, kidney, brain, red blood cells	Mostly liver; small amounts in muscle and kidney
Half-life in blood	About 17 hours — rises and falls faster	About 47 hours — stays up longer after an injury
Non-liver causes of a high value	Exercise, muscle injury or disease, heart attack, hemolysis, hypothyroidism, celiac disease	Few — strenuous exercise and muscle disease raise it a little
Typical liver pattern	Higher than ALT in alcohol-related disease (ratio 2 or more) and in cirrhosis of any cause	Higher than AST in fatty liver disease, viral hepatitis and most drug injury
Best use	Read alongside ALT for the ratio; with CK when muscle is suspected	The screening and follow-up test for liver injury

Reference ranges are the reviewed catalog ranges for adults; your laboratory's printed range may differ slightly.

Why ALT is the more specific liver test

Both enzymes move amino groups between molecules inside cells; they leak into the blood when cell membranes are damaged. ALT is found at high concentration almost only in liver cells, so a raised ALT nearly always means the liver. AST is spread across liver, heart, skeletal muscle, kidney, brain and red cells — a marathon, a muscle injury, a heart attack or a sample that hemolyzed in the tube can raise it with a perfectly healthy liver.

That is why the ALT is the number used to screen for liver disease and to follow it, and why guidelines for abnormal liver tests start from a raised ALT. Current reference limits are lower than many labs still print — about 30 U/L in men and 25 in women — because the older limits were set in populations that included people with undiagnosed fatty liver.

What the AST/ALT ratio tells you

The De Ritis ratio (AST divided by ALT) is a pattern clue, not a diagnosis. Alcohol damages the mitochondria where much of the liver's AST sits and depletes the vitamin B6 that ALT needs, so alcohol-related liver disease classically shows an AST about twice the ALT, with both usually under 300 U/L. Fatty liver disease, viral hepatitis and most medication injuries do the opposite — ALT above AST, a ratio under 1.

As scarring (fibrosis) advances from any cause, the ratio drifts upward and crosses 1; an AST above ALT in someone with known fatty liver or hepatitis C is a reason to check for cirrhosis. The ratio is one of the inputs to the FIB-4 score (with age and platelets) that decides who needs elastography.

When a high AST is not the liver

An AST that is raised out of proportion to the ALT — or an isolated AST elevation — points away from the liver. A creatine kinase (CK) settles whether muscle is the source (heavy training in the previous three days, a fall, a statin myopathy, an inherited muscle disease). A hemolyzed sample raises AST and LDH together with potassium; the lab usually notes it. Hypothyroidism and celiac disease are the two quiet causes worth testing for when nothing else explains it.

How the two are followed

A first mild elevation (under twice the upper limit) is repeated in four to eight weeks after alcohol, supplements and hard exercise are stopped; a third of such results are normal on repeat. If they stay up, the next set is a hepatitis B and C screen, ferritin and iron saturation, a lipid panel and glucose, and — if the ratio or platelets suggest it — a FIB-4 and ultrasound. Values above five times the upper limit, or any rise with jaundice, are looked at promptly.

How do you test AST and ALT?

Prices are cash-pay; every order adds one $6 lab processing fee. Physician authorization is included; no insurance or referral needed.

Test or panel	Type	Price	Fasting	Results
Biological Age Panel	Panel · 3 tests	$59.99	Yes	1–3 business days
Gout Panel	Panel · 3 tests	$62.99	Yes	2–4 business days
General Wellness Panel	Panel · 4 tests	$49.99	Yes	1–3 business days
Liver Function Panel	Test · 7 biomarkers	$19.49	No	1–3 business days
Comprehensive Metabolic Panel	Test · 14 biomarkers	$21.49	Yes	1–3 business days

Common questions

Which is worse, high AST or high ALT?

Neither is 'worse' — the pattern matters. A high ALT with a lower AST almost always means the liver (usually fatty liver, a virus or a medication); a high AST with a normal ALT often is not the liver at all. The size of the elevation and the ratio between the two, together with bilirubin, albumin and platelets, tell you how serious it is.

What does an AST/ALT ratio over 2 mean?

In someone with raised enzymes, an AST at least twice the ALT points to alcohol-related liver disease, particularly when both are under 300 U/L and the GGT is also raised. A ratio above 1 in fatty liver or viral hepatitis suggests scarring has advanced. A high ratio with normal-range enzymes means little on its own.

Can exercise raise AST and ALT?

Yes — strenuous or unaccustomed exercise raises AST (and CK) within a day and can keep it up for three to seven days; ALT rises less and later. A blood test drawn after a hard workout can show an 'abnormal liver panel' with a healthy liver, which is why the repeat is done after 72 hours without heavy exercise.

What is a dangerous level of AST or ALT?

Values more than 10–15 times the upper limit (roughly above 500–1,000 U/L) mean acute injury — viral hepatitis, a drug or toxin (acetaminophen overdose), a blocked blood supply, or a passing gallstone — and are assessed the same day, especially with jaundice, confusion or a rising INR. Mild elevations (under 2–3 times) are common and are repeated before anything is concluded.

Sources

Educational content, not a diagnosis. Lab results are one input; a clinician interprets them with your history and exam.